Field of the Invention
This invention relates generally to treads for retreaded tires, and more particularly, to precured treads having transverse grooves to provide venting of gases within the tread.
Description of the Related Art
When retreading tires, it is generally known to replace the tread with a new precured tread. In doing so, a tread is generally formed having grooves arranged along an outer side of the tread. In particular instances, longitudinal grooves may also be arranged along an inner or bottom side of the tread to provide one or more tread wear layers, where different tread features are exposed as the tread wears depthwise into a thickness of the tread.
During the retreading process, a new precured tread is arranged around a pre-existing or used tire carcass, typically with bonding material arranged between the new tread and the tire carcass to promote adhesion between the tread and the tire carcass. The retread tire is bonded together by vulcanizing or curing the tire assembly, thereby causing the bonding material to adhere the new tread to the tire carcass.
The longitudinal voids, if closed to the outer tread surface during the curing operation, can experience an internal pressure different from the pressure applied to the outer tread surface due to the air trapped within the closed longitudinal voids. This pressure differential may increase when vacuum is applied to a curing membrane in which the tire is situated and/or when pressure is applied to the tire by the autoclave. This pressure differential can cause distortion of the tread elements in the cured tire.
Additionally, during use of such prior retreaded tires, air trapped in the hidden grooves on the inner or bottom side of the tread may at various times be at a different pressure from atmospheric, either because of inertia, an increase or decrease in temperature, and/or from deflection of the tread, thereby causing undesirable pressure differentials in the hidden voids under the tread. Any such pressure differential can cause distortion of the tread elements in the cured tire.
Accordingly, there is a need for venting the air contained beneath or within the tread during the retreading process and during tire operation. Further, such venting, if applied in a manner described in certain embodiments of this invention, could result in a cooling effect to significantly lower running temperatures of the tread ribs or elements thereof during tire operation.